Polishing Pad and Multi-Head Polishing System

ABSTRACT

A chemical mechanical polishing system includes a polishing pad, a platen to support the polishing pad, and two rotatable carrier heads configured to hold two substrates against the polishing pad at the same time. Each carrier head includes a retaining ring. Two actuators sweep the two carrier heads laterally across the polishing pad between positions closer to and farther from the center axis. A polishing surface of the polishing pad includes a center region with a first grooving pattern and an annular region with a second grooving pattern different than the first grooving pattern. A radius of the center region is equal to or less than a distance from a center axis of the platen to a closest outer edge of the two retaining rings when the carrier heads are in the closer positions.

TECHNICAL FIELD

This disclosure relates to a polishing pad in a multi-head polishing system.

BACKGROUND

An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive, or insulative layers on a silicon wafer. One fabrication step involves depositing a filler layer over a non-planar surface and planarizing the filler layer. For certain applications, the filler layer is planarized until the top surface of a patterned layer is exposed. A conductive filler layer, for example, can be deposited on a patterned insulative layer to fill the trenches or holes in the insulative layer. After planarization, the portions of the metallic layer remaining between the raised pattern of the insulative layer form vias, plugs, and lines that provide conductive paths between thin film circuits on the substrate. For other applications, such as oxide polishing, the filler layer is planarized until a predetermined thickness is left over the non-planar surface. In addition, planarization of the substrate surface is usually required for photolithography.

Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is typically placed against a rotating polishing pad. The carrier head provides a controllable load on the substrate to push it against the polishing pad. An abrasive polishing slurry is typically supplied to the surface of the polishing pad.

The polishing pad typically includes two layers, including a cover layer and a softer backing layer. The cover layer can be a polyurethane with pores, e.g., IC-1000, and the backing layer can be a more compressible material, e.g., SUBA-4. However, a variety of other pad structures are possible, e.g., single-layer polishing pads. The polishing pad is typically grooved in to distribute the polishing slurry evenly below the substrate. Typical grooving patterns include concentric circular grooves and orthogonal linear grooves that form a rectangular cross-hatched pattern.

SUMMARY

In some CMP systems, multiple substrates are polished simultaneously on a single polishing pad. Although the substrates are oscillated laterally across the polishing pad during the polishing operation, there can be a region near the center of the polishing pad that is not contacted by the substrate and not used for polishing. However, by-products of the polishing operation such as debris or slurry can collect in the grooves in the center of the pad. When the polishing pad is rinsed, these by-products can be released back to the portion of the pad used for polishing, causing scratching or other defects in a subsequent polishing operation. However, by having a different grooving pattern in the center region of the pad, release of the by-products can be reduced.

In one aspect, a chemical mechanical polishing system includes a polishing pad, a platen to support the polishing pad, the platen rotatable about a center axis, a rotatable first carrier head configured to hold a first substrate against the polishing pad, the first carrier head including a first retaining ring, a rotatable second carrier head configured to hold a second substrate against the same polishing pad at the same time that the first carrier head holds the first substrate against the polishing pad, the second carrier head including a second retaining ring, a first actuator to sweep the first carrier head laterally across the polishing pad while the first substrate contacts the polishing pad, a second actuator to sweep the second carrier head laterally across the polishing pad while the second substrate contacts the polishing pad, and a controller configured to cause the first actuator to sweep the first carrier head between a first position closer to the center axis and a second position farther from the center axis and to cause the second actuator to sweep the carrier head between a third position closer to the center axis and a fourth position farther from the center axis. A polishing surface of the polishing pad includes a center region and an annular region surrounding the center region, the center region having a first grooving pattern and the annular region having a second grooving pattern different than the first grooving pattern, and wherein a radius of the center region is equal to or less than a distance from the center axis to a closest outer edge of the first retaining ring when the first carrier head is in the first position and the second retaining ring when the second carrier head is in the third position.

Implementations can include one or more of the following features. The first grooving pattern may be configured to provide a lower resistance to outward slurry flow than the second grooving pattern. The polishing surface in the center region may have no grooves. The polishing surface in the center region may have at least one groove, and the first grooving pattern may differ from the second grooving pattern. The at least one groove may include a spiral groove. The spiral grove may spiral in a first direction from outside inwardly, and the controller may be configured to cause the motor to rotate in the first direction while the first substrate and the second substrate are being polished. The polishing surface in the center region may have a first plurality of grooves having a first pitch and the polishing surface in the annular region may have a second plurality of grooves having a second pitch that is less than the first pitch. The annular region may have a plurality of concentric circular grooves. The annular region may have a first plurality of linear grooves and a second plurality of linear grooves orthogonal to the first plurality of linear grooves. The radius of the center region may be equal to the distance from the center axis to the closest outer edge. The radius of the center region may be less than the distance from the center axis to the closest outer edge. The first position and the third position may be equidistant from the center axis. The polishing system may include a track, a first carriage supported by the track, and a second carriage supported by the track. The first carrier head may be suspended from the first carriage and the second carrier head may be suspended from the second carriage. The track may form an arcuate path over the polishing pad.

Implementations can include one or more of the following potential advantages. Release of by-products from a center region of the polishing pad can be reduced. Defects on the substrate can be reduced, and yield can be increased.

The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other aspects, features and advantages will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a plan view of an example of a polishing apparatus.

FIG. 2 illustrates a schematic cross-sectional view of an example of a polishing apparatus.

FIG. 3 illustrates a plan view of a polishing pad illustrating possible positions for the substrates.

FIGS. 4A-4D are a plan views of a polishing pad illustrating example grooving patterns.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 is a plan view of a chemical mechanical polishing apparatus 100 for processing one or more substrates. The polishing apparatus 100 includes a polishing platform 106 that at least partially supports and houses one or more polishing stations 124. The polishing apparatus 100 also includes a multiplicity of carrier heads 126, each of which is configured to carry a substrate. The multiplicity of carrier heads 126 includes at least two carrier heads 126A, 126B. Each polishing station 124 is adapted to polish a substrate that is retained in a carrier head 126.

The polishing apparatus 100 can also include one or more load cups 122 adapted to facilitate transfer of a substrate between the carrier heads 126 and a factory interface (not shown) or other device (not shown) by a transfer robot 110. The load cups 122 generally facilitate transfer between the robot 110 and each of the carrier heads 126.

Each polishing station 124 includes a polishing pad 130 supported on a platen 200 (see FIG. 2). The polishing pad 110 can be a two-layer polishing pad with an outer polishing layer and a softer backing layer. A plurality of grooves 213 can be formed in the polishing surface 212 of the polishing pad 110 (see FIG. 2).

At least one of the polishing stations 124 is sized such that a plurality of carrier heads 126A, 126B can be positioned simultaneously over the polishing pad 130 so that polishing of a plurality of substrates can occur at the same time in the polishing station 124. For example, each of the plurality of carrier heads 126A, 126B can hold a single substrate, and each carrier head 126A, 126B that is within the same polishing station can lower its substrate into contact with the same polishing pad 130. Thus, a plurality of substrates, e.g., one per carrier head, can be polished simultaneously with the same polishing pad.

In some implementations, the polishing station 124 can accommodate two carrier heads 126A, 126B. Thus, two substrates can be polished simultaneously on the same polishing pad 130. However, in some implementations the polishing station could be constructed to accommodate three or more carrier heads.

The carrier heads 126 are coupled to a carriage 108 that is mounted to an overhead track 128. The overhead track 128 allows each carriage 108 to be selectively positioned around the polishing platform 106. The configuration of the overhead track 128 and carriages 108 facilitates positioning of the carrier heads 126 selectively over the polishing stations 124 and the load cups 122. In the embodiment depicted in FIG. 1, the overhead track 128 has a circular configuration (shown in phantom) which allows the carriages 108 retaining the carrier heads 126 to be selectively rotated over and/or clear of the load cups 122 and the polishing stations 124. It is contemplated that the overhead track 128 may have other configurations including elliptical, oval, linear or other suitable orientation.

Each polishing station 124 of the polishing apparatus 100 can include a port 218 to dispense polishing liquid 220 (see FIG. 2), such as abrasive slurry, onto the polishing pad 130. Each polishing station 124 of the polishing apparatus 100 can also include a pad conditioning apparatus 132 to abrade the polishing pad 130 to maintain the polishing pad 130 in a consistent abrasive state.

FIG. 2 is a partial cross-sectional view of a polishing station 124 of FIG. 1. The polishing station 124 includes the platen 200 on which the polishing pad 130 can be mounted. The platen 200 is coupled by a shaft 202 to a motor 204, e.g., a DC induction motor, to rotate the platen 200 and the polishing pad 130 about a rotational axis.

Each of the carrier heads 126A, 126B is coupled to a rotary motor 214A, 214B by a drive shaft 208A, 208B. Thus, each motor 214A, 214B can independently rotate the respective carrier head 126A, 126B about a rotational axis relative to the polishing pad 130 and platen 200.

The polishing system 100 is configured to sweep the carrier heads 126A, 126B laterally across a polishing surface 212 of polishing pad 130. The lateral sweep is in a direction parallel to the polishing surface 212. The lateral sweep can be a linear or arcuate motion. In particular, each motor 214A, 214B, drive shaft 208A, 208B and carrier head 126A, 126B can be suspended by a carriage 108A, 108B that is supported by the track 128. Each carriage 108A, 108B, can be independently driven along the track by an associated actuator 106A, 106B. Each actuator 106A, 106B can be a DC motor.

Each carrier head 126A, 126B is operable to hold a substrate 216A, 216B against the polishing pad 130. Each carrier head 126A, 126B can have independent control of the polishing parameters, for example pressure, associated with each respective substrate.

Each carrier head 126A, 126B can include a retaining ring 224A, 224B to retain a substrate 216A, 216B below a flexible membrane 230. Each carrier head 126A, 126B includes one or more independently controllable pressurizable chambers 228 defined by the membrane 230, which can apply independently controllable pressurizes to associated zones on the flexible membrane 230 and thus on the substrate 216A, 216B. Although only one chamber per carrier head is illustrated in FIG. 2 for ease of illustration, there could be two chambers or more chambers, e.g., three or five chambers.

Optionally, each carrier head 126A, 126B can be coupled by the shaft 208A, 208B to a linear actuator to independently lift or lower the respective carrier head 126A, 126B in the Z direction relative to a polishing surface 212 of the polishing pad 130. Alternatively, the Z direction actuation can be provided by an actuator, e.g., a pressurizable chamber, within the carrier head 126A, 126B.

In operation, when an even number of substrates, such as two semiconductor substrates 216A, 216B, are provided to the load cups 122 of the polishing module 100 (FIG. 1), each carrier head 126A, 126B is positioned over the load cups 122 to facilitate transfer of the two substrates 216A, 216B from the load cups 122 to the carrier heads 126A, 126B. Once the substrates 216A, 216B are retained in the carrier heads 126A, 126B, the carrier heads 126A, 126B are positioned over the polishing pad 130 by action of the carriages 108. Each carrier head 126A, 126B is urged toward the polishing surface 212 of the polishing pad 130. The motor 204 rotates the platen 200, the rotary actuators 214A, 214B rotate the carrier heads 126A, 126B, and the actuators 106A, 106B cause the carrier heads 126A, 126B to sweep across the polishing surface 212.

A controller 190, such as a programmable computer, is connected to each motor 204, 214A, 214B to independently control the rotation rate of the platen 120 and the carrier heads 126A, 126B. For example, each motor can include an encoder that measures the rotation rate of the associated drive shaft. Similarly, the controller 190 is connected to each actuator 106A, 106B to independently control the lateral motion of each carrier head 126A, 126B. For example, each actuator can include a linear encoder that measures the position of the carriage along the track 128.

Referring to FIG. 3, in operation the polishing pad 130 rotates (as shown by arrow 302) about a center axis 304. The carrier head 126A oscillates along the track 128 between position A1 closer to the center axis 304 and position A2 farther from the center axis 304, and the carrier head 126B oscillates along the track 128 between position B1 closer to the center axis 304 and position B2 farther from the center axis. This leaves a center region 310 that does not contact the substrate 10 or retaining ring 224 during the polishing operation.

The radius R can be calculated by subtracting the substrate radius and the retaining ring width from the minimum distance D between the head location 306 and the center axis 304. The distance D can be known from the dimensions of the polishing apparatus, e.g., the size of the platen 120 and the location of the track 128, as well as the head sweep parameters in the polishing recipe stored by the controller 190. In general, the radius R can be between 50 and 200 mm, although as noted it depends on the dimension of the polishing apparatus and the sweep of the carrier heads.

In some implementations, the minimum distance D is 254 mm, the substrate radius is 150 mm and the retaining ring radius is 25 mm, resulting in a radius R=79 mm (254−150−25). In some implementations, the minimum distance D is 284 mm, the substrate radius is 150 mm and the retaining ring radius is 25 mm, resulting in a radius R=109 mm (284−150−25).

The center region 310 of the polishing pad has a different grooving pattern than the annular region 312 surrounding the center region 310. The annular region 312 can extend to the edge 314 of the polishing pad 130. The grooving pattern in the annular region 312 can be uniform across the annular region 312. In some implementations, the center region 310 does not have grooves. In some implementations, the grooving pattern in the center region 310 is configured to provide a lower resistance to outward slurry flow than the grooving pattern in the annular region 312. In some implementations, the grooving pattern in the center region 310 is configured to urge slurry outwardly from the center axis 304.

Referring to FIG. 4A, in some implementations, the annular region 312 has a plurality of concentric circular grooves 320, but the center region 310 has no grooves. The grooves 320 are concentric around the center axis 304. The dimensions of the grooves 320 in the annular region 322 can be consistent with the IC-1010 polishing pad.

Referring to FIG. 4B, in some implementations, the annular region 312 has a plurality of linear grooves 330, 332, but the center region 310 has no grooves. The linear grooves 330 are orthogonal to the linear grooves 332, so that the grooves 330, 332 form a rectangular pattern.

Referring to FIG. 4C, in some implementations, the annular region 312 has a plurality of concentric circular grooves 340, and the center region 310 has a spiral groove 342. The grooves 340 are concentric around the center axis 304. The dimensions of the grooves 340 in the annular region 312 can be consistent with the IC-1010 polishing pad. The spiral groove 342 rotates, from the outside inwardly, in the same direction of the direction of rotation 302 of the polishing pad 130. This configuration tends to urge the slurry outward from the center axis 304. This can reduce accumulation of slurry or by- products in the center region during polishing, and can help clean out the center region during rinsing.

Referring to FIG. 4D, in some implementation, the annular region 312 has a plurality of linear grooves 350, 352, and the center region 312 has a spiral groove 354. The linear grooves 350 are orthogonal to the linear grooves 352, so that the grooves 350, 352 form a rectangular pattern. The spiral groove 354 rotates, from the outside inwardly, in the same direction of the direction of rotation 302 of the polishing pad 130. This configuration tends to urge the slurry outward from the center axis 304. This can reduce accumulation of slurry or by-products in the center region during polishing, and can help clean out the center region during rinsing.

In some implementations, the center region 310 and the annular region 312 have a geometrically similar pattern and the pitch of the grooves in annular region is smaller than the pitch of the grooves in the center region. This could be implemented with either concentric circular grooves or orthogonal linear grooves.

The above described polishing apparatus and methods can be applied in a variety of polishing systems. Although a plurality of polishing stations are illustrated in FIG. 1, there could be just a single polishing station. The polishing pad can be a shape other than circular. The polishing layer can be a standard (for example, polyurethane with or without fillers) polishing material, a soft material, or a fixed-abrasive material. Terms of relative positioning are used; it should be understood that the polishing surface and substrate can be held in a vertical orientation or some other orientations.

While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. 

What is claimed is:
 1. A chemical mechanical polishing system, comprising: a polishing pad; a platen to support the polishing pad, the platen rotatable about a center axis; a rotatable first carrier head configured to hold a first substrate against the polishing pad, the first carrier head including a first retaining ring; a rotatable second carrier head configured to hold a second substrate against the same polishing pad at the same time that the first carrier head holds the first substrate against the polishing pad, the second carrier head including a second retaining ring; a first actuator to sweep the first carrier head laterally across the polishing pad while the first substrate contacts the polishing pad; a second actuator to sweep the second carrier head laterally across the polishing pad while the second substrate contacts the polishing pad; and a controller configured to cause the first actuator to sweep the first carrier head between a first position closer to the center axis and a second position farther from the center axis and to cause the second actuator to sweep the carrier head between a third position closer to the center axis and a fourth position farther from the center axis; wherein a polishing surface of the polishing pad includes a center region and an annular region surrounding the center region, the center region having a first grooving pattern and the annular region having a second grooving pattern different than the first grooving pattern, and wherein a radius of the center region is equal to or less than a distance from the center axis to a closest outer edge of the first retaining ring when the first carrier head is in the first position and the second retaining ring when the second carrier head is in the third position.
 2. The system of claim 1, wherein the first grooving pattern is configured to provide a lower resistance to outward slurry flow than the second grooving pattern.
 3. The system of claim 1, wherein the polishing surface in the center region has no grooves.
 4. The system of claim 1, wherein the polishing surface in the center region has at least one groove, and the first grooving pattern differs from the second grooving pattern.
 5. The system of claim 4, wherein the at least one groove comprises a spiral groove.
 6. The system of claim 5, wherein the spiral grove spirals in a first direction from outside inwardly, and wherein the controller is configured to cause the motor to rotate in the first direction while the first substrate and the second substrate are being polished.
 7. The system of claim 1, wherein the polishing surface in the center region comprises a first plurality of grooves having a first pitch and the polishing surface in the annular region comprises a second plurality of grooves having a second pitch that is less than the first pitch.
 8. The system of claim 1, wherein the annular region comprises a plurality of concentric circular grooves.
 9. The system of claim 1, wherein the annular region comprises a first plurality of linear grooves and a second plurality of linear grooves orthogonal to the first plurality of linear grooves.
 10. The system of claim 1, wherein the radius of the center region is equal to the distance from the center axis to the closest outer edge.
 11. The system of claim 1, wherein the radius of the center region is less than the distance from the center axis to the closest outer edge.
 12. The system of claim 1, wherein the first position and the third position are equidistant from the center axis.
 13. The system of claim 1, further comprising a track, a first carriage supported by the track, and a second carriage supported by the track, wherein the first carrier head is suspended from the first carriage and the second carrier head is suspended from the second carriage.
 14. The system of claim 13, wherein the track forms an arcuate path over the polishing pad. 